Recent medical studies have indicated that a diet containing the U.S. recommended daily allowance (RDA) of calcium may be effective in preventing or mitigating osteoporosis, and also possibly high blood pressure and colon cancer. There is therefore great public interest in the consumption of food products which will supply the recommended daily allowance of calcium. Dairy products have traditionally been recognized as good sources of calcium. Yogurt in particular is frequently consumed by those persons who may be most in need of an adequate calcium intake, for example, people who are dieting, and pregnant or middle aged women. An eight ounce serving of fruit-flavored low fat yogurt provides only approximately 345 mg of calcium, however, in comparison to the U.S. RDA of 1,000 mg. It therefore is desirable to supplement the natural calcium content of yogurt.
Serious practical difficulties in incorporating calcium supplement into dairy products have been encountered, however, because most calcium salts have very low solubility in milk, which has a pH of about 6.8. In milk itself, up to 60-70% of the calcium exists as insoluble colloidal calcium phosphate associated with the casein micelles. Added calcium salts therefore tend to settle out, frustrating attempts to maintain uniform dispersions during manufacture. This problem is compounded by the fact that generally the yogurt base may not be agitated during the incubation period. Thus, in the manufacture of yogurt using vat incubation the required lack of agitation during incubation allows a substantial portion of the calcium salt to settle to the bottom of the vat. The salt then must be scraped off the bottom of the vat and blended into the yogurt, a process which not only is impractical using conventional yogurt manufacturing equipment, but also is likely to adversely affect the texture of the product.